Multi-center, double-blind, placebo-controlled, parallel group comparison study to investigate the safety, tolerability and efficacy of BAY 12-9566,a cartilage metalloproteinase inhibitor. This is compared to placebo,in the treatment of patients with mild to moderate osteoarthritis of the knee. over three months. BAY 12-9566 will be compared to placebo in terms of safety, tolerability and efficacy in a three month, multicenter randomized study.